Conventional roof trusses in the shape of a triangle have long been used to support ordinary peaked roofs having an inverted V-shape, with a single ridge or peak. Internal diagonals joining the peak to the horizontal lower base chord of each truss obstruct the open space inside the truss, and minimize the usefulness of the enclosed area directly under the roof.
Conventional roof framing trusses are highly economical when used for the construction of plain peaked roofs, but do not lend themselves to the construction of gambrel roofs. Moreover, an "inclined chord" highway bridge type truss may have horizontal lower chords and successively inclined upper chords forming a polygon-shaped outline which may resemble a gambrel, but such a truss is obstructed by many vertical and diagonal internal truss members, thus filling the volume under any overlying roof with truss members, which prevent practical use of the space for normal purposes.
In addition, trusses supporting the roofs of buildings enclosing piles of granular materials such as salt, sand, grain or powdered chemicals require a large open space extending to the maximum available clear height under the roof peak and extending laterally to the walls of the structure, without obstruction by horizontal truss chords or other truss members. Horizontal spans up to 60 feet are useful in material storage buildings of this kind, but costly roof supporting trusses of steel have been required to support roof spans of this size, making a sturdy and economical long span gambrel roof truss highly sought after.